System information in Third Generation Partnership Project (3GPP) Universal Mobile Terrestrial System (UMTS) Long Term Evolution (LTE) systems includes parameters needed by a wireless communication mobile station (MS), hereafter also referred to as user equipment (UE), for correct operation. This information is grouped into different information blocks including a Master Information Block (MIB) and several System Information Blocks (SIB). Generally, UEs are expected to use the currently valid system information set at all times. To manage changes of system information (SI), the notion of a modification period is used. When the network needs to change a SI parameter, a change indication is first transmitted for a duration known as a modification period. The actual changed SI is transmitted in a subsequent modification period. This framework ensures that a UE in idle mode or in connected mode gets an indication of the SI change and subsequently reads the changed SI. However, if a SI change occurs when a UE is attempting to establish a connection, the UE may use old SI.
Potential problem scenarios are discussed below where the SI change period and radio resource control (RRC) connection establishment overlap. The first scenario resulted from a discussion of 3GPP technical document R2-082942.
In one scenario illustrated in FIG. 1, a UE receives an SI change indication and a page at the same time. Alternatively, a similar problem arises if the UE decides to originate very shortly after receiving a SI change indication. The ensuing random access channel (RACH) attempts cross the modification period boundary and because of the time required for the UE to read SI, a UE RACH attempt that occurs after the modification period boundary will use old SI. This may be problematic as the PHICH duration or resource may have changed leading to failure after the UE enters connected mode. The same problem results, though less frequently, from the following circumstances: a change of other MIB parameters; cell barring status may have changed; a change in time division duplex (TDD), UL/DL split; a change in the RACH parameters (e.g., root sequence, PRACH resources, preamble split, random access (RA) response window, preamble_trans_max, . . . ) leading to failed RACH attempts and interference to other UEs; access class barring may have been switched on which the UE would be violating.
In another scenario illustrated in FIG. 2, a UE originates in a modification period where the SI is being modified, but the origination is started before the UE's paging occasion, so the UE is unaware of the SI change at the time of origination. This scenario requires the UE to continue monitoring paging for the SI change indication, which is contrary to Proposal 1 of 3GPP technical document R2-082942. Assuming that the UE receives the SI change indication, the UE still cannot receive the changed SI and all the problems mentioned above are possible.
In yet another scenario illustrated in FIG. 3, a UE interrupts RACH attempts when the modification period boundary is reached, and the UE reads the new SI, and then restarts the RACH attempts. Particularly, at the modification period boundary the UE suspends T300 and starts reading MIB, SIB1, SIB2. After the modification period boundary, the UE does not RACH until reading MIB, SIB1, SIB2. After the modification period boundary, UE does not receive/act on a RACH response until a RACH is sent after reading MIB, SIB1, SIB2. This is to avoid the following situation where the UE sends the RACH before the modification period boundary, and receives a RACH response with an UL grant after the modification period boundary. The UE should not send message 3 before reading SI, but the UL grant is not valid for that long. So the UE has to simply ignore the RACH response. The UE sends the RACH again after reading MIB, SIB1, SIB2. In FIG. 3, the UE restarts T300 and continues the RACH procedure after reading MIB, SIB1 & SIB2. The problem with this solution is that each time there is a SI change no UE can perform any UL transmissions until reading the SI. Reading the SI can take more than a second and ˜300 ms for the most critical information. This duration then becomes a blackout period for the system resulting in wasted capacity and delay to various applications in UE. This problem becomes particularly acute when the SI is changed relatively frequently for load management purposes during peak hours.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.